Fair Value Measurements - Financial instruments not carried at fair value (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments		$ 172,500	$ 142,300
Deposit liabilities		1,030,290	1,116,233
Notes payable and debt	[1]	3,210,063	2,647,677
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments		172,453	142,271
Deposit liabilities		1,030,290	1,116,233
Notes payable and debt		3,210,063	2,647,677
Financial Liabilities		4,240,353	3,763,910
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments		182,454	153,173
Deposit liabilities		1,258,115	1,337,406
Notes payable and debt		3,476,673	2,813,257
Financial Liabilities		$ 4,734,788	$ 4,150,663

[1] "In Use/Outstanding" data represent September 30, 2017 and December 31, 2016 accreted values.